Human semen
quality may rise and fall in seasonal variation, with the best quality being
produced in the winter and spring.

Research suggests that semen produced during that time has a greater concentration of
sperm of which a higher percentage are fast moving and appear normal when
looked at under a microscope.

Researchers
took semen samples from 6,477 men who had been referred with their partner to a
fertility clinic in Israel. Men who had sperm counts in the normal range averaged
71 million sperm per millilitre in spring, which fell to a low of 64 million in
autumn. Although total sperm motility was greatest during the summer months,
the percentage of fast-moving sperm, thought to increase the chances of
fertilisation, was highest in winter.

In men with
lower than normal sperm concentration seasonal variation was less marked. The
highest percentage of sperm with normal morphology was in the spring, and a
slight trend towards greater motility was also observed during this time. However neither the
concentration of sperm or the percentage of fast-moving sperm altered significantly
between seasons.

The findings have not been directly linked
with increased conception rates in the winter although Israeli birth statistics
do show an increase in births during the autumn. The authors of the paper suggest that 'the winter and spring semen patterns are compatible with
increased fecundability and may be a plausible explanation of the peak number
of deliveries during the fall'.

The majority of previous studies on
seasonal variations in sperm production have been performed in animals. In
pigs, sperm cell development seems to be affected by temperature and in hamsters some of the genes
controlling seasonal production have been identified.

Although this study is one of the first to show
seasonal sperm quality variation in humans, the authors are confident enough to suggest that men with
low sperm concentration should seek fertility treatment in spring and autumn.

However, speaking to Reuters, urologist Dr Edmund
Sabanegh, director of the Centre for Male Fertility in Cleveland, USA, who was
not involved in the study, disagreed. 'We
would continue to encourage [patients] to try regardless of the season, and
they may benefit from interventions or treatments', he said.

The research was published in the American Journal of
Obstetrics and Gynecology.

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